Indoor location technology innovation for small cells – will GPS be enough?

In the future, small cells may have an increasing reliance on GPS. What happens if the system were to fail or the signal not be reliably available indoors? What technology leaps can be taken to address this? We spoke to one innovative startup that is pioneering new techniques to solve the problem.

I spoke with Rich Lee, CEO of iPosi, a Denver US startup that’s developing advanced technology to determine small cell location. Using Pletronics standard small cell TCXO's, it also provides an accurate timing source for LTE and other situations.

What’s your primary application for small cells?

Our focus with small cells is for wide area indoor location – small cells fitted with our technology can determine their own position to within 20-30 metres, even when indoors or tucked away in a street canyon with limited view of the sky. This is particularly important for location based services, such as E911 emergency calling. We can also provide an accurate clock reference for both frequency and phase which is essential for CDMA and LTE small cells, especially when part of a HetNet.

We see a growing interest in location based services from web content and search companies who seek to increase the relevance of their services for smartphone devices. GPS reception directly by smartphones often isn’t good indoors or in urban streets, and small cells can be used to deliver a better service in these situations.

How does your solution work?

Our solution capitalises on the continuing development and multi-national evolution of GPS and GNSS. GNSS (Global Navigation Satellite Systems) includes not only the familiar GPS system operated by the US but also similar systems launched by Russia (GLONASS) and in the future Europe (Galileo) and China (COMPASS), as well as regional systems such as Japan (QZSS). Once complete (mostly within the next five years), there will be more than 300 civilian-accessible signals transmitting from over 100 international satellites across multiple global systems. Range measurements are further augmented by separate geostationary satellites sending correction data to further improve accuracy (such as WAAS/EGNOS). These are extremely reliable systems and are already heavily relied on by aircraft, ships and automobiles to navigate with pinpoint accuracy 24x7 around the globe.

Our technology analyses selected sets of these different signal sources to determine position. Unlike traditional standard GPS receivers, we don’t need to constrain the solution by mandatorily locking on to multiple signals at the same time but can acquire a fix by receiving if necessary with just one signal at a time. We ultimately need to decode four satellites, but we can spread individual satellite signal observations over time based on patented methods that offset the bias arising from time-spread measurements, thus we are not constrained to simultaneously receive the traditional minimum of four satellites, all with sufficient power. This is imperative for operating indoors since satellite signals will vary remarkably. Unlike a car SatNav or aircraft, we also have the benefit of knowing that the small cell doesn’t move, which helps reduce certain technical constraints while still serving moving mobile devices’ location needs. When indoor, GNSS satellite signals are of less power and fluctuate 100-fold in strength, so we’ve had to design how to deal with the issue of extracting position from an array of non-uniform signals.

As with consumer GPS receivers, we provide an innovative form of receiver “assistance” (telling the receiver what characteristics of the incoming signals so as to more sensitively, quickly and accurately locate them since they are deeply shrouded by noise). We can also quickly reacquire position in the event of a power disruption or as a routine check of current position which is an important verification process for E911 for instance. If the device has been moved when switched off, for example a customer has relocated it to his summer home, we can deal with that too.

The solution requires additional firmware and hardware within the small cell design, but we believe the benefits outweigh any extra costs incurred. We’ve worked closely with a leading frequency source supplier, Pletronics, who not only supply their high specification TCXO but have provided us with extensive technical characterization data which is key to overall performance. As we move forward, we expect to become more closely integrated with the system hardware design which we believe will enhance value and competitive leadership for our customers.

Which services would benefit from this technology?

The best known and easiest business case for location services is the E911 emergency call, mandated today in the US, Canada and Japan by the regulator. Residential femtocells in these countries are fitted with GPS receivers today to ensure that when making an E911 call the location is known, and is accurately reported to the appropriate emergency dispatch center. Typically the locations of macrocell sites installed by an operator are manually recorded by installation teams/planners, and that data is used (supplemented by location fixing technology) to determine and report the callers location.

Expanding beyond E911, with large numbers of public access indoor and street canyon small cells being deployed, a more automated solution to determine and report location is extremely beneficial to wireless operators. We see our technology being most attractive to operators deploying small cells, to better use the radio resource (reduce interference with surrounding infrastructure) and conserve spectrum (maintain tight frequency control to avoid spilling over into adjacent channels). It also ensures roaming rules are respected and is not used where E911 arrangements are not in place or is outside the license area of the operator.

Emergency location is also becoming important in other regions. Russia and a European partnership have formed to offer eCall for which all new cars will have automatic crash reporting fitted from 2015. We believe this bodes well for emergency call in those locations for small cell applications as well.

In addition, we are seeing growing interest in location services worldwide. Small cells have an important part to play especially in areas where smartphones can’t directly determine their position through GPS alone.

How would the solution be used for synchronization?

Newer generation small cells also need to be synchronized to within a standardized tolerance of time and phase. All wireless technologies specify a tight tolerance with respect to frequency – and the tolerance depends on the particular technology deployed. Poor alignment of frequency leads to dropped calls during hand-over between cells since the mobile expects the serving stations to be close in terms of transmit frequency. Time and phase sync are particularly important for CDMA and the new LTE small cells, - a feature that GSM or UMTS small cells don’t require. Several timing sources may be used of which this may be one. We deliver better than 50 parts per billion frequency (ppb) tolerance specified for small cells in addition to tight time and phase tolerances of less than 1 microsecond.

This leads to reduced spectrum management costs through more accurate synchronization. A HetNet can carry more traffic if it is well tuned, with less interference between the small cells and overlapping macrocells.